1. Field of the Invention
The present invention relates generally to an apparatus and method for authentication/copy protection of optical storage medium, and the optical storage medium.
2. Brief Description of the Related Art
As information storage medium in the multimedia environment, optical discs have been widely used for storage of music, movies, and software due to their high storage capacity. The optical disc has several advantages over other storage media in that mass-production is possible at a low price, and the quality of the information thereon is not degraded upon copying the disc repeatedly.
Because low-price copy machines have been released to the market, the digital information on the optical disc can be copied perfectly and easily, resulting in enormous economic loss due to illegal copying of the information such as music, movies, and software.
Thus, many methods have been proposed to inhibit or limit the illegal copying of the optical discs. As one of them, Korean Patent Application S/N. 97-32576, proposed by these inventors, discloses a signal recording method for optical disc having a copy-protection function and copy protection of the optical disc based on the recording method.
In the method, a non-standard symbol, which is made by shifting or delaying one bit of a chosen standard symbol or codeword by a predetermined length, is written on a specified area of the optical disc. The optical disc turns out to be genuine if the non-standard symbol is reproduced as either of two standard symbols (hereinafter referred to as xe2x80x9ctarget symbolsxe2x80x9d) whenever it is read out repeatedly.
In cases of CD-ROM or CD-DA driver, signals read out from the optical discs are fed to an EFM (Eight to Fourteen Modulation) demodulator, and are then error-corrected in a CIRC (Cross Interleave Reed-Solomon Code) fashion. When the non-standard symbols are processed by the ECC (Error Correction Code) decoder of the CIRC type, even if either of the two target symbols are reproduced from the non-standard symbols, the two target symbols may be considered an error symbol and corrected by the ECC decoder. Thus, the desired authentication of the optical disc may fail.
Accordingly, a general objective of the present invention is to solve the above mentioned problems and to provide an apparatus and method for authentication/copy protection of optical storage medium that is compatible with existing drivers for optical storage media.
A more specific object of the present invention is to provide an apparatus and method for authentication/copy protection of optical storage medium that enables any optical storage medium driver to perform the authentication operation without installation of additional software/hardware.
Another specific object of the present invention is to provide an apparatus and method for authentication/copy protection of optical storage medium that enables correct authentication operation even when a set of symbols containing non-standard symbols undergoes error-correction by an ECC decoder after a read-out operation.
Another specific object of the present invention is to provide an apparatus and method for authentication/copy protection of optical storage medium that enables a correct decision as to whether or not the optical storage medium is genuine by preserving standard symbols, which are obtained through repetitive read-out of the non-standard symbol from the optical storage medium, during in the ECC decoding process.
Another specific object of the present invention is to provide an apparatus and method for authentication/copy protection of optical storage medium in which symbols that are needed for the authentication operation are obtained due to intentional modification of parity symbols; the modification being determined in consideration of the error correction capability of an ECC decoder.
These and other objects are achieved by providing a method of recording data in a copy protected manner on an optical disk, comprising modifying at least a first signal in data such that said modified first signal is reproduced as one of a plurality of target signals prior to error correction decoding, error correcting encoding said data prior to said modifying such that said reproduced target signals remain unchanged after error correction decoding, and writing said modified encoded data on an optical storage medium.
These and other objects are further achieved by providing a method of recording data in a copy protected manner on an optical disk, comprising choosing at least one pair of standard symbols from a list containing a plurality of pairs of standard symbols, each pair of standard symbols in said list including a first symbol and a second symbol differing by a number of zeros between consecutive ones, first generating first and second codes, said first code including at least one of said first symbol in said chosen pair of standard symbols and said second code including at least one of said second symbol in said chosen pair of standard symbols, second generating first and second parity symbols for said first and second codes, respectively, first modifying said first parity symbols, second modifying said first symbols in said first code, and writing said modified first code on an optical disk.
These and other objects are still further achieved by a copy protected recording medium having a data structure stored thereon, comprising a test area storing test data, said test data including at least one modified first signal, said modified first signal having been modified such that when said modified first signal is reproduced, said modified first signal is reproduced as one of at least two target signals.
These and other objects are also achieved by the copy protected recording medium, wherein said test data includes a first code, said first code including said modified first signal and modified first parity symbols, said modified first parity symbols including at least one symbol in common with parity symbols of a first target code and a second target code, said first and second target codes being a same code except said first target code includes said first target signal at predetermined position and said second target code includes said second target signal at said predetermined position.
These and other objects are additionally achieved by providing an apparatus for recording data in a copy protected manner on an optical disk, comprising a shifter modifying at least a first signal in data such that said modified first signal is reproduced as one of a plurality of target signals prior to error correction decoding, an encoder error correcting encoding said data prior to said modifying such that said reproduced target signals remain unchanged after error correction decoding, and a mastering apparatus writing said modified encoded data on an optical storage medium.
These and other objects are further achieved by providing an apparatus for recording data in a copy protected manner on an optical disk, comprising an encoder generating first and second parity symbols for first and second codes, respectively, said first code including at least one of a first symbol and said second code including at least one of a second symbol, said first symbol and said second symbol differing by a number of zeros between consecutive ones, said encoder modifying said first parity symbols, a shifter modifying said first symbols in said first code, and a mastering apparatus writing said modified first code on an optical disk.